Digital signal editing apparatus

ABSTRACT

A novel digital signal recording and reproducing apparatus is disclosed in which an audio digital signal is recorded and reproduced alone or together with a video signal in a video tape recorder. If the sampling frequency of the audio signal is not an integral multiple of the vertical synchronous signal of the video signal, the audio signal is divided among fields in accordance with a predetermined regularity, and then the field information for identifying the number of samples of the audio digital signal is added and recorded for each field. At the time of reproduction, the field information is read to identify the number of samples of the audio digital signal, thus picking out only the audio signal excepting the redundant portions. In adding or inserting a signal of tape 2 to tape 1, the reproduced signal of tape 2 is divided and recorded again among the fields on the basis of the field information obtained from the reproduced signal of tape 1 in such a manner as to satisfy the regularity with which the audio signal already recorded in tape 1 is divided among the fields.

This is a division of application Ser. No. 847,213 filed Apr. 2, 1986,now U.S. Pat. No. 4,772,959.

BACKGROUND OF THE INVENTION

The present invention relates to a digital signal recording andreproducing apparatus which is capable of recording and reproducing anaudio digital signal alone or together with a video signal in a videotape recorder (hereinafter referred to as the VTR).

In the conventional apparatus in which an audio digital signal isrecorded in a VTR, the sampling frequency of the audio signal isselected to be an integral multiple of the vertical synchronous signalof the video signal to record the audio digital signal in apredetermined number of samples during one vertical scanning period(hereinafter referred to as a "field"). In the case of a PCM audioprocessor according to the EIAJ (Electronic Machinery IndustryAssociation of Japan) standards, for instance, the audio samplingfrequency for the VTR of an NTSC system is set to the frequency of44,056 KHz, that is 735 times higher than the vertical synchronoussignal (60×1000/1001≈59.94 Hz). In this case, the audio digital signalof 735 samples per channel is recorded in a signal field of the VTR.

There may be some cases, however, where the audio sampling frequency isnot an integral multiple of the vertical synchronous signal. In a PCMrecorder used for business purposes for which a sampling frequency of 48KHz is recommended according to AES (Audio Engineering Society)Standards, for example, an audio digital signal of 800.8 samples isrecorded for each channel in a field, dividing one sample, if recordedin a VTR of an NTSC system. When an audio digital signal of 800.8samples is recorded in a field this way, it is necessary to divide asample, thereby complicating the circuit configuration. Further, anediting process for each field becomes difficult.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an apparatus forrecording and reproducing an audio digital signal in a video taperecorder, wherein even if the sampling frequency of the audio signal isnot an integral multiple of the vertical synchronous signal of the videosignal, the original audio signal in continued form is capable of beingrestored by recording and reproduction, and there occurs no dropouts ofthe sample of the audio digital signal before or after the editing pointwhen the editing process is made for each field.

According to the present invention, there is provided a digital signalrecording and reproducing apparatus comprising means for dividingsamples of the audio digital signal for respective fields according to apredetermined rule, means for generating field information foridentifying the number of samples of the audio digital signal for eachfield, which number is different for each field, means for recording theaudio digital signal combined with the field information for each field,means for detecting the field information at the time of reproduction,means for restoring the original continuous audio signal in accordancewith the field information detected, and means for dividing samples ofthe audio digital signal input on the recording side on the basis of thefield information on the reproduction side.

Assuming that several recorded tapes are edited by use of two or moreVTRS, when the signal of one tape (tape 2) is added to or inserted intofor recording in the other tape (tape 1), the field information obtainedfrom the reproduced signal of tape 1 is used to restore the reproducedsignal of tape 2 into the original continuous audio signal. After that,the reproduced signal of tape 2 is divided again for respective fieldsthereby to correspond to the field division of the reproduced signal oftape 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a digital signal recording andreproducing apparatus according to an embodiment of the presentinvention.

FIG. 2 is a diagram showing a signal format of the audio digital signalin an embodiment of the present invention.

FIG. 3 is a diagram showing a field allocation the audio digital signaland the field information according to an embodiment of the presentinvention.

FIG. 4 is a timing chart for explaining the circuit operation of adigital signal recording and reproducing apparatus according to anembodiment of the present invention.

FIG. 5 is a block diagram showing a configuration for an editing processusing two digital signal recording and reproducing apparatuses accordingto an embodiment of the present invention.

FIG. 6 is a timing chart for explaining the editing operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Description will be made below of an apparatus for recording andreproducing an audio digital signal in a VTR in the case where an audiosampling frequency is not an integral multiple of the verticalsynchronous signal of the video signal.

Assume that the audio sampling frequency is 48 KHz as described in theBACKGROUND OF THE INVENTION, and a VTR of an NTSC system is used, as anexample. In the VTR of NTSC system, the vertical synchronous signal is60×1000/1001 Hz, and therefore 800.8 samples of the audio digital signalconverted by the sampling frequency of 48 KHz are recorded in each fieldof a channel. It is, however, not expedient to divide one sample torecord the divided sample in a field in view of the complication of thecircuit configuration and editing processes. According to the embodimentunder consideration, therefore, as shown in FIG. 3, five fields arehandled as a unit, so that 800 samples of the audio digital signal arerecorded in one of them, and 801 samples in the remaining four fields.This is possible in view of the fact that a total of 4004 samples ofaudio digital signal are recorded in each five fields. Various signalformats are conceivable for the audio section recorded in a field, ofwhich the signal format shown in FIG. 2 will be used as an example forexplanation of the embodiment under consideration.

An analog audio signal is converted into an audio digital signal by 48KHz sampling and 16-bit linear quantization, and is comprised of audiosignal pulses D₀, D₁, D₂, . . . , D₇₉₈, D₇₉₉ in 800-sample fields, and801 samples including D₀, D₁, D₂, . . . , D₇₉₈, D₇₉₉, D₈₀₀ in 801-samplefields. The 16-bit signal of each sample is divided into symbols of mostsignificant 8 bits and the least significant 8 bits. The sample D₀, forexample, is represented by the most significant symbol D_(0U) and theleast significant symbol D_(0L).

When a signal format is constructed after division into symbols, thesignals are rearranged (interleaved) in order to facilitate errorcorrection by dispersing burst dropouts. In FIG. 2, each field iscomprised of 67 blocks, so that the sample D₀ (D_(0U), D_(0L)) isarranged in the block 0, sample D₁ (D_(1U), D_(1L)) in the block 34,sample D₂ (D_(2U), D_(2L)) in the block 2, and so on. In the case wherea field includes 67 blocks each of which in turn is comprised of 12samples (24 symbols) of audio digital signal, each field is comprised of804 samples (1608 symbols). As a result, 4 samples (8 symbols) and 3samples (6 symbols) of extraneous areas are generated for the 800-samplefields and 801-sample fields respectively. These areas are defined inID1 to ID6 or ID1 to ID8 in FIG. 2 and may be used as information areasfor other than the audio digital signal as index data (ID). In thisembodiment, a part of these information areas (hereinafter referred toas "the ID areas") is used to record field information for detectingwhether an audio digital signal belongs to the 800-sample fields(hereinafter referred to as "the leap fields") or the 801-sample fields.Various methods are possible for setting and recording the fieldinformation in the ID areas. As shown in Example 1 of FIG. 3, forinstance, the field information which is 0 for leap fields and 1 forother fields is recorded by use of a bit of LSB of ID1 on the signalformat shown in FIG. 2. In Example 2, on the other hand, the fieldinformation " 00" and "FF" are recorded in hexadecimal form in the leapfields and other fields respectively by using all the 8 bits of ID1. Instill another example, as shown in an Example 3 of FIG. 3, 0 is recordedin the n-th leap field, 1 in the (n+1)th field, 2 in the (n+2)th field,3 in the (n+3)th field and 4 in the (n+4)th field. In this way, the 3bits of ID1 are used for repeated recording of 0 to 4. The embodimentunder consideration will be explained below with reference to the mostsimple case of Example 1.

As explained above, an audio digital signal is arranged in each block,and the field information is set in the ID areas. Two groups of errorcorrection codes (ECC), ECC1 and ECC2 (each having four symbols), areused as shown in FIG. 2. The generation series of each error correctioncode are not shown. If ECC1 is formed from the symbols of the sameblock, however, ECC2 is generated from symbols of a plurality of blocks.For example, the data of the 24 symbols including D_(0U), D_(0L),D_(67U), . . . , D_(737U), D_(737L) of the block 0 and the four symbolsincluding P₀, Q₀, R₀ and S₀ of the block 0 are used to form the foursymbols (P₀ ', Q₀ ', R₀ ', S₀ ') of ECC1 of block 0. On the other hand,data of a symbol selected from every other blocks including D_(0U) ofblock 0, D_(4L) of block 2, and D_(75U) of block 4 are used to form thefour symbols P₄₈, Q₅₀, R₅₂, S₅₄ of ECC2 of the blocks 48, 50, 52 and 54from 24-symbol data in the even-numbered blocks from block 0 to block46. The other symbols of ECC1 and ECC2 are also formed by following thesame rule as mentioned above. In forming ECC2 beyond the block 66 ingeneration series, however, the process is returned to block 0. In theforegoing description, the data of ECC2 is included in generating ECC1,and therefore ECC2 is formed before ECC1. After generating an errorcheck code in this way, addition is made to each block of two symbols ofblock sync signal (SYNC), a symbol of block address signal (ADRO toADR66) and a symbol of error detection code for the block address signal(EDC) as shown in FIG. 2, so that the signals from blocks 0 to 66 arerecorded in a field in accordance with the recording sequence shown inFIG. 2.

A block diagram of a digital signal recording and reproducing apparatusaccording to the embodiment under consideration is shown in FIG. 1. Theoperation of this apparatus shown in the block diagram of FIG. 1 will beexplained below with reference to the timing chart of FIG. 4.

In the digital signal recording and reproducing apparatus shown in FIG.1, a master clock is generated in a clock generator 12 from thehorizontal sync signal produced from the VTR. Specifically, a PLL (phaselocked loop) circuit is used actually. First, the timing of processingvarious signals is determined at a timing generator 13 by the verticalsynchronous signal from the VTR. The various timings thus determinedinclude the timing of starting to generate an error check code in FIG.4, the timing of recording the recording signal, and the timing ofstarting an error correction period.

The analog audio input signal is stored in RAMs of a memory 2temporarily after being converted into an audio digital signal by anA.D. converter 1. There are two RAMs, each having the capacity to storea field of audio digital signal and an error correction code. While, anoutput signal (audio digital signal) of the A/D converter 1 is beingwritten in one of the RAMs, the audio digital signal that had been reada field before is read from the other RAM thereby to generate the errorcheck codes ECC2 and ECC1 in an encoder 3. The error correction codesECC1, ECC2 thus generated are written in the same RAM, so that a signalformat as shown in FIG. 2 is formed excluding the redundant parts of thesignal SYNC etc. on the RAM. Then, in accordance with the recordingsequence shown in FIG. 2, the signal is compressed along a time axis foreach block and read from the RAM. The signal thus read takes anintermittent form to enable SYNC, ADD0 to ADD66 and EDC to be insertedat the encoder 3. After the redundant parts are inserted at the encoder3, the recording signal is modulated and applied to the VTR. Awell-known modulation process such as FM, MFM or 3PM may be used.

Under normal recording operation, the vertical sync signal from the VTRis used to generate a field identification signal A which becomes highin level for each five fields, at the timing generator 13, and the fieldinformation generator 5 generates an audio field signal A and fieldinformation in such a manner that a high-level field of the fieldidentification signal A becomes a leap field. An address counter in theaddress signal generator 4 is controlled by the audio field signal A.The output signal of 800 samples produced from the A/D converter 1 arewritten in the RAMs of the memory 2 when the field identification signalA is high in level, and the same output signal of 801 samples when thefield identification signal A is low in level. At the same time, thesignal of the ID area including the field information and the outputsignal of the A/D converter 1 are written by time division in the RAM.The field information, as shown by Example 1 of FIG. 3, is set in such amanner that LSB of ID1 is zero when the field identification signal A ishigh in level, and 1 when it is low in level.

The vertical sync signal and the audio field signal A have a phasedifference ΔT, 2ΔT, . . . as shown in FIG. 4 due to the leap fields. Theaudio input signal, however, is divided for each field by this audiofield signal A. Let the period of the vertical synchronous signal Be T,the field period of the leap field be T₁, and the field period of otherfields than the leap fields be T₂. The relationship given by theequation below is held.

    5T=T.sub.1 +4T.sub.2

    800T.sub.2 =801T.sub.1

ΔT is expressed by the equation below.

    T=T.sub.2 -T

These equations are easily obtained from the fact that 1/T=60×1000/1001,1/T₂ =48000/800 and 1/T₂ =48000/801.

In a reproduction mode, on the other hand, the reproduced signal isdemodulated at a decoder 8, and temporarily stored in a RAM in a memory7. The memory 7, like the memory 2 of the recording system, has twoRAMs, each having the capacity of one field. The demodulated reproducedsignal is written in one of the RAMs, and then, errors are corrected atan error corrector 9. In the meantime, a corrected audio digital signalprior to one field is read out of the other RAM, converted into theoriginal time series, and produced to a D/A converter 6.

In the error correction process, ECC1 corrects an error of the signal inthe block first of all, followed by the error correction by ECC2 duringthe high-level error-correction period in FIG. 4. In the case of anerror symbol that cannot be corrected, an error flag is formed, andafter interpolation, an analog audio output signal is produced throughthe D/A converter 6. Under reproduction operation, the decision of aleap field is performed after the error correction. The fieldinformation is read from the ID area, and if it is found to be 0 by thefield information detector 11, a leap field is decided, while if thefield information is found to be 1, a field other than the leap fieldsis decided, so that the field identification signal B and the audiofield signal B are generated. The audio field signal becomes high inlevel when a leap field is decided. The address signal generator 10controls the memory 7, and generates an address for the RAMs in such amanner as to apply 800 or 801 samples of the audio digital signal exceptfor the ID areas to the D/A converter 6 in accordance with the audiofield signal B. In this way, an original continuous audio signal isproduced.

When audio signals reproduced from several VTRs are mixed or edited intoa master tape, the signal already recorded in the tape and a signal tobe newly recorded therein are cross-faded with each other in order tomake natural connections of sounds before and after the editing point.In this method, the rate at which these signals are added to each otheris changed gradually for recording in a predetermined section before andafter the editing point. In this case, it is necessary to reproduce thesignal already recorded in the tape and record it in the same positionof the same tape. For this reason, the VTR according to the embodimentunder consideration is equipped with a reproduction head at a positionadvanced by time t (described in FIG. 4) from the recording head. Theoperation of this configuration will be explained below.

The reproduced signal shown by the hatched line in FIG. 4 is demodulatedand the error thereof corrected along the arrow of dotted line, so thatthe signal of the original time series (audio output signal) is appliedto a D/A converter 6 and to a buffer memory 14 at the same time. Inorder to absorb the jitter of clocks of the recording and reproducingsystems, the clocks on the reproduction side are used for writing thereproduced signal in the buffer memory 14, while the clocks on therecording side are used for reading therefrom. As a result, thereproduced signal is rendered synchronous with the clock on therecording side through the buffer memory 14.

Generally in recording an analog audio signal, the memory 2 is suppliedwith an audio digital signal through the A/D converter 1 and iscontrolled by a field identification signal A in such a manner that thehigh-level section makes up a leap field, thus producing a recordingsignal along the arrow shown by solid line in FIG. 4. In recording thereproduced signal again in the same tape, on the other hand, thereproduced signal, after the error thereof is corrected, is applied tothe recording side through the buffer memory 14 and to the memory 2 inplace of the output of the A/D converter 1. In this case, the signalflow is shown by the dotted arrow in FIG. 4.

In controlling the leap field on the recording side, the audio fieldsignal A is produced by the field identification signal B obtained fromthe reproduced signal for producing an address for the memory 2 in orderto meet the regularity of the signal already recorded. If the timedifferent t between the recording and reproduction heads mentioned aboveis set to the same length as the time required before the reproducedsignal is applied through the reproduction system, the buffer memory 14and further through the recording system to be recorded in the sametape, then the reproduced signal can be always recorded again in thesame position of the same tape in relation with the already-recordedsignal. Also, the audio field signal A is generated by the fieldidentification signal B in a manner to coincide with the audio fieldsignal B, and therefore the number of samples of the audio signal forrecording always coincides with that of the audio signal for thereproduced signal for the field at the same time point. As aconsequence, the regularity of the audio signal between the fields ismaintained also in the boundary between the already-recorded signal andthe signal to be recorded again.

Now, a method of editing by use of two digital signal recording andreproducing apparatuses and two VTRs according to the present embodimentwill be explained with reference to FIG. 5.

Reference will be taken to the case in which two recorded tapes are usedand the signal recorded in one tape is added to or inserted into theother tape by recording.

Tape 1 is loaded on VTR 1, and tape 2 on VTR 2. As shown in FIG. 5, VTR1is coupled with a digital signal recording and reproducing apparatus15A, and VTR2 with a digital signal recording and reproducing apparatus15B. The digital signal recording and reproducing apparatuses 15A, 15Bare the same as the apparatus 15 shown in FIG. 1. The numerals of eachblock in the apparatuses 15A, 15B are affixed with A and B with thenumerals of blocks shown in FIG. 1, respectively.

Assume that the m-th field of tape 2 is recorded immediately followingthe n-th field of tape 1. The VTRs are reproduced separately, and afterdetermining respective editing points, the VTRs are driven reverselyfrom the editing points. The vertical synchronous signal of VTR1 issupplied to VTR2, and the two VTRs are driven in synchronization witheach other in such a manner that the respective editing points thereofcoincide with each other. An example of the timing of the reproducingsignals in this case is shown in FIG. 6. The reproduced signal in thiscase indicates an audio digital signal returned to the original timeseries after error correction. Also, the forward end of the field of thereproduced signal has no phase difference with the vertical synchronoussignal only for the leap fields.

The (n-1)th field of tape 1 is the leap field, and so is the m-th fieldof tape 2. Therefore, in the case where the VTRs are driven in such away that the (n+1)th field of tape 1 and the m-th field of tape 2 comeat the same time point as shown in FIG. 6, the reproduced signal of tape1 and the reproduced signal of tape 2 have different timings of theforward end of each field. The (n-1)th field of tape 1 and the (m-2)thfield of tape 2, for instance, have the timing difference of 2ΔT, whilethe timing of the n-th field of tape 1 is different by (4ΔT-ΔT=3ΔT) fromthe (m-1)th field of tape 2. Also, the phase difference between thesamples of the respective reproduced signals is always 2ΔT. This dependson the editing point of tapes 1 and 2. Both VTRs 1 and 2 are based onthe vertical synchronous signal of VTR1, and the reproduced signals ofVTR1 and VTR2 contain a jitter respectively. As a result, there exists aphase difference due to the leap field and a jitter at the time ofdriving between the two reproduced signals.

For applying the reproduced signal of VTR2 to the recording system ofVTR1 and recording in tape 1, it is necessary to compensate for thephase difference due to the leap field and the jitter that occurs at thetime of driving.

As shown in FIG. 5, the reproduced signal of VTR2 returned to theoriginal time series from the memory 7B is sent to the buffer memory 14Aof the digital signal recording and reproducing apparatus 15A for theabove-mentioned compensation. In the buffer memory 14A, the clock of thereproduction system of the digital signal recording and reproducingapparatus synchronous with the reproduced signal of VTR2 is used forwriting, while the clock of the recording system of the digital signalrecording and reproducing apparatus 15A is used for reading out of thememory. Therefore, through this buffer memory 14A, the reproduced signalof VTR2 is synchronized with the clock of the recording system of thedigital signal recording and reproducing apparatus 15A. In the editingoperation, it is necessary to maintain the regularity of leap fieldbetween the signal already recorded and the newly recorded signal as inthe case of recording the reproduced signal again as mentioned above.For this purpose, on the basis of the field information obtained fromthe reproduced signal of the VTR1, the fields of the recording signal ofthe digital signal recording and reproducing apparatus 15A areconfigured. Specifically, in the digital signal recording andreproducing apparatus 15A, the field identification signal A and theaudio field signal A of the recording system of the digital signalrecording and reproducing apparatus 15A are produced in accordance withthe field identification signal B generated from the reproduced signalof VTR1, so that the number of the samples of the audio signal alwayscoincides at the field of the same time point between the reproducedsignal of VTR1 and the recording signal sent to VTR1.

This process is taken after the editing point, and the process forrecording the reproduced signal of VTR1 again is taken before theediting point. Take the case of FIG. 6 as an example. Before the editingpoint, the signal of the (n-1)th field of the reproduced signal of VTR1is applied through the buffer memory 14A to the memory 2A thereby tomake up the (n-1)th field of the recording signal of the VTR1. Insimilar manner, the n-th field of the recording signal of VTR1 is madeup of the 801 samples of the n-th field of the reproduced signal ofVTR1. In the fields after the editing point, however, the reproducedsignal from the VTR1 and VTR2 have different numbers of samples of audiodigital signal making up a field. Therefore, in configuring a field ofthe recording signal of VTR1, the 800 samples of the m-th field of thereproduced signal of VTR2 and the one sample at the top of the (m+1)thfield thereof are combined to form 801 samples for the (n+1)th field. Inthis case, the field information of the (n+1)th field is assumed tobe 1. In the (n+2)th field, on the other hand, the 800 samples exceptingthe leading sample of the (m+1)th field of the reproduced signal of VTR2are combined with the leading sample of the (m+2)th field to form 801samples. The field information is assumed to be 1 in this case also. The(n+3)th field is subjected to the same processing as the (n+2)th field.The (n+4)th field, which is a leap field, is configured of 800 samplesexcepting the leading sample of the (m+3)th field, and the fieldinformation of0 is assumed to be involved. As mentioned above, in thecase where the data recorded in tape 2 is added to or inserted into thedata recorded in tape 1, the reproduced signal of tape 2 is dividedagain for each field to satisfy the regularity of the leap field of thetape 1, and field information is newly generated and recorded in tape 1.When the tape 1 thus edited is reproduced, the regularity of the leapfields of audio digital signal is maintained between the fields beforeand after the editing point. The phase of the field of the audio signaland the vertical synchronous signal coincide with other only once foreach five fields, but by dividing the reproduced signal of tape 2 againfor each field, the editing by field becomes possible.

It will be understood from the foregoing description that according tothe digital signal recording and reproducing apparatus of the presentinvention, even when the number of samples of the audio digital signalis different from one field to another, it is possible to prevent anytime disorder or abnormal noises due to dropouts of audio samples or thelike in the joint of fields in the recording and reproducing operation.

What is claimed is:
 1. A digital signal apparatus for editing videotapes on which, when a sampling frequency of an audio signal isdifferent from an integral multiple of a field frequency of a videosignal, an audio digital signal is divided into fields each containing anumber of sampling units of the audio digital signal, and informationfor identifying the number of sampling units of the audio digital signalas well as the audio digital signal contained in the sampling units arerecorded in each field, said apparatus comprising:means for reproducingthe sampling number information as well as the audio digital signal froma first video tape; means for reproducing the sampling numberinformation as well as the audio digital signal from a second videotape; means for re-dividing the audio digital signal reproduced from thesecond video tape into each field in accordance with the sampling numberinformation of each field reproduced from the first video tape; andmeans for recording the re-divided audio digital signal together withthe sampling number information reproduced from the first video tapebeginning from a predetermined edit point of the first video tape.